Diaziridines

A review of three-membered rings with two heteroatoms has been published which includes diaziridines, diazirines, and oxaziridines.  

At 100 °C, under nitrogen, the N-carbamoyldiaziridines (343 R = Ph, R = cyclohexyl or Bu ) and (343 R = 3-CIC6H4 or 4-MeOC6H4, R = cyclohexyl) isomerize to (345), which were characterized by n.m.r. and by X-ray crystallography.A dipolar intermediate (344) was postulated in the reaction. The hydrolysis of either (343) or (345) gave acetophenone together with a substituted semicarbazide. 

Partial separation of enantiomeric AW -dimethyldiaziridines has been achieved by chromatography on triacetylcellulose.  

Photolysis of the tetrazolones (338 R = Pr or Me) in MeCN or pentane gave the corresponding diaziridinone (339). Photolysis of (340) gave (341) in a process which is thermally reversible.  

Preparative separations or enrichments of the enantiomers of (344) and (345) have been achieved by liquid chromatography on triacetylcellulose. Almost pure (+)-(344) and (+)-(345) were isolated. 

The mass spectra of (346) and related compounds have been reported. 

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Oxidopyridazinium betaines isomerize photochemically into pyrimidin-4(3H)-ones (33). Irradiation of 3-oxidopyridazinium betaine or 1-oxidophthalazinium betaine in water affords similarly the corresponding pyridazin-3(2H)-one (35) and phthalazin-l(2H)-one derivative (37). However, photolysis in acetonitrile affords stable diaziridines (34) and (36) which can be converted in the presence of water to the final products (35) and (37) (Scheme 12) (79JCS(P1)1199). 

Photolysis of pyridazine IV-ethoxycarbonylimide results in the formation of the pyrrole derivative (56). The rearrangement is postulated to proceed via a diaziridine, followed by ring expansion to the corresponding 1,2,3-triazepine derivative and rearrangement to a triazabicycloheptadiene, from which finally a molecule of nitrogen is eliminated (Scheme 19) (80CPB2676). 

Diaziridine derivatives (42) can be obtained from tetrazoles of type (41). 

Photodecomposition of A -l,2,3-triazolines gives aziridines. In cyclohexane the cis derivative (304) gives the cis product (305), whereas photolysis in benzene in the presence of benzophenone as sensitizer gives the same ratio of cis- and trans-aziridines from both triazolines and is accounted for in terms of a triplet excited state (70AHC(ll)i). A -Tetrazo-lines are photolyzed to diaziridines. 

Diaziridines also show slow nitrogen inversion, and carbon-substituted compounds can be resolved into enantiomers, which typically racemize slowly at room temperature (when Af-substituted with alkyl and/or hydrogen). For example, l-methyl-3-benzyl-3-methyl-diaziridine in tetrachloroethylene showed a half-life at 70 °C of 431 min (69AG(E)212). Preparative resolution has been done both by classical methods, using chiral partners in salts (77DOK(232)108l), and by chromatography on triacetyl cellulose (Section 5.08.2.3.1). 

The introduction of a second heteroatom (other than sulfur) does not change drastically the absorption characteristics of small heterocycles. Oxaziridine and diaziridine are still transparent to light of wavelengths above 220 nm (Section 5.08.2.3.2). 

In the diaziridine field many compounds are known bearing N-YL, A/-alkyl and A-acyl groups, but here no dramatic changes in reactivity are caused by A-substituents. N-Aryldiaziridines are underrepresented. The ring carbon is in the oxidation state of a carbonyl compound or, in the diaziridinones (5) and the diaziridinimines (6) that of carbonic acid. In single cases, diaziridine carbon bears chlorine or fluorine. 

Fused diaziridines may be bridged from either C to N as in (7) or from N to N as in (8). The latter type usually contains the A-substituents cis to each other. 

Whereas oxaziridine and diaziridine were partial subjects of comprehensive theoretical studies on cyclic compounds (73MI50800), diazirine and some of its simple derivatives were the special target of quantum chemical investigations. Since diazirine, the lowest molecular weight heterocycle, has only five atoms and is of high symmetry, there was a chance for ab initio calculations, which followed some semiempirical studies. 

Structural data of a diaziridine come from gas phase electron diffraction measurements (74CC397). The N—N bond of 3-methyldiaziridine (24) is longer than in hydrazine (1.449 A) the C—N bond distances in (24) and in diazirine are nearly equal (1.479 versus 1.482 A),... 

S.08.2.3.1 NMR investigations on oxaziridines and diaziridines, configurational stability at nitrogen... 

NMR investigations in the diaziridine field also led to the problem of inversion stability at nitrogen. Further investigations paralleled those of oxaziridines NMR investigation in solution (67CB1178) was followed by preparative separation of invertomers and finally preparation of optically active individuals. 

The c/s-fused diaziridines (31a) and (31b) are also an equilibrium system, interchanging exo and endo positions of methyl and ethyl groups. The NMR spectrum shows two methyl peaks at 0 °C, coalescing to a single sharp peak at 75 °C. The ethyl group shows the sharp characteristic quartet-triplet splitting pattern at 75 °C (74JOC3187). 

Diaziridine (33) was obtained with more than 90% optical purity by separation of the a-phenylethylamine salts (76IZV1898). 

Simple oxaziridines and diaziridines do not absorb in the near UV. Lack of absorption was one argument to distinguish between true three-membered ring structures and unsaturated open chain isomers like nitrones or hydrazones. 

On the basis of IR data the basicity of some diaziridines was discussed. The basicity of the spirodiaziridines (36) increased on alkylation of one nitrogen from pAT = 4.6 (R = H) to pK = 6.4 (R = Bu"). pK values of diaziridines alkylated on both nitrogens were always below 5.0 (69IZV1847). 

Mass spectra of the same diaziridines were reported later (74JOU1140). Whereas in longer alkyl side chains of diaziridines the typical amine degradation by n -1 carbon atoms predominates, successive elimination of NH and methyl was observed in (37a). The 1-methyl compound (37b) undergoes competitive elimination of NH and MeN. 

The PE spectra of simple diaziridines exhibit two bands at lower ionization potentials these are assumed to arise from removal of an electron from one or other of the lone pair MOs. An E arrangement of the two N-bound hydrogens in 3,3-dimethyldiaziridine (37a) is assumed, since the difference of the ionization potentials (0.51 eV) is much smaller than in the fused diaziridine (42) (1.40 eV) which necessarily has the Z configuration (73HCA1614). 

It was reported only recently that A-methyl transfer from an oxaziridine to an amine occurs with formation of an N—N bond (79JA6671). N—N bond forming reactions with A-unsubstituted oxaziridines had been found immediately after discovery of this class of compound (64CB2521) and have led to simple hydrazine syntheses (79AHC(24)63). Secondary amines like diethylamine or morpholine are A-aminated by (52) in the course of some minutes at room temperature with yields exceeding 90% (77JPR195). Further examples are the amination of aniline to phenylhydrazine, and of the Schiff base (96) to the diaziridine (97). 

Diaziridines, discovered in 1958, six years after the oxaziridines, were almost immediately realized to be structural analogs of oxaziridines. Like these they showed oxidizing properties unexpected for other classes of organic nitrogen compound. Properties in common with oxaziridines include the rearrangement to open chain isomers on heating above 100 °C (for several diaziridines), and their hydrolytic behavior in acidic media, which leads to carbonyl compounds with conservation of the hetero-hetero bond. 

There are differences in the high temperature behavior. While oxaziridines almost always isomerize to acid amides, a similar reaction of diaziridines, which should lead to amidines, has not been observed. Sensitivity towards bases, often encountered in oxaziridines, is observed only in some special substituted diaziridines. The tendency of some classes of oxaziridines to transfer the nitrogen function also lacks in the diaziridine field. On homolytic reactions of diaziridines there are only a few observations. 

Substitution with conservation of the three-membered ring is more versatile in diaziridine chemistry, because the ring is somewhat more stable and because of the presence of two nitrogen atoms. 

Diaziridinones and diaziridinimines, discovered about 10 years later, add much to the versatility of the diaziridine field, especially due to valence isomerizations. 

Alkylation of diaziridines with simple alkylating agents has never been attempted, because N-alkyldiaziridines are as easily obtained by ring synthesis as the unsubstituted ones. There... 

Aryldiaziridines (125), difficult to obtain by standard diaziridine syntheses, were prepared by arylation with 2,4-dinitrofluorobenzene (72JOC2980). 

Chloral forms well-crystallized adducts (126) with diaziridines containing at least one NH group (B-67MI50800). Carbonyl addition products to formaldehyde or cyclohexanone were also described. Mixtures of aldehydes and ammonia react with unsubstituted diaziridines with formation of a triazolidine ring (128). Fused diaziridines like (128) are always obtained in ring synthesis of diaziridines (127) from aldehyde, ammonia and chloramine. The existence of three stereoisomers of compounds (128) was demonstrated (76JOC3221). Diaziridines form Mannich bases with morpholine and formaldehyde (64JMC626), e.g. (129). 

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